1. Field of the Invention
The present invention relates to a memory/logic mixed semiconductor device in which memory and logic devices are fabricated on a semiconductor substrate, and to a method for manufacturing the same.
2. Description of the Background Art
In the field of recent system LSIs, memory/logic mixed semiconductor devices are attracting attention in which large-capacity high-speed memory devices and logic devices are constructed on the same semiconductor substrate. Among them, as to semiconductor devices mounted with DRAMs suitable for large capacity applications, devices in which silicide films are formed within memory cells are developed to achieve higher speed memory devices.
Japanese Patent Application Laid-Open No. 2001-127270 (hereinafter referred to as a first patent document) discloses an example of such a memory/logic mixed semiconductor device having silicide films within memory cells. According to the technique described in the first patent document, silicide films are formed on source/drain regions and gate electrodes of transistors in both of a DRAM portion where DRAM resides and a logic portion where a logic device resides. Techniques about formation of silicide films are disclosed in Japanese Patent Application Laid-Open Nos. 2000-269482 and 8-31769 (1996) and International Publication WO98/42009.
In the memory/logic mixed semiconductor device described in the first patent document, as shown in FIG. 6 attached to it, the silicide film in the upper surfaces of source/drain regions in the DRAM portion and the silicide film in the upper surfaces of source/drain regions in the logic portion have the same thickness. Therefore, when the silicide film in the logic portion is formed thick to achieve higher speed of the logic device, then the silicide film in the DRAM portion, too, forms thick, which increases the leakage current of capacitors electrically connected to the source/drain regions. This deteriorates data storage characteristic of the DRAM. On the other hand, when the silicide film in the DRAM portion is formed thin to reduce the capacitor leakage current, then the silicide film in the logic portion also forms thin, which lowers operating speed of the logic device.